Showing papers by "Petr Vogel published in 1997"
TL;DR: In this paper, the authors examine isovector and isoscalar correlations in an exactly solvable model based on the algebra SO(8) and examine Gamow-Teller strength and double β decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes.
Abstract: We examine isovector and isoscalar neutron-proton correlations in an exactly solvable model based on the algebra SO(8). We look particularly closely at Gamow-Teller strength and double β decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton quasiparticle random phase approximation (QRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller β+ strength on isospin changes in a dramatic and unfamiliar way, actually increasing as neutrons are added to an N=Z core. Renormalization eliminates the well-known instabilities that plague the QRPA as the phase transition is approached, but only by unnaturally suppressing the isoscalar correlations. Generalized BCS theory, on the other hand, reproduces the Gamow-Teller strength more accurately in the isoscalar phase than in the usual isovector phase, even though its predictions for energies are equally good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar side of the phase transition.
108 citations
TL;DR: In this paper, the observed abundances of these isotopes are entirely consistent with neutrino-induced nucleosynthesis, strongly arguing for a supernova r-process site and placing stringent constraints on the freezeout radius and dynamic time scale of the r process.
Abstract: If the r process occurs deep within a type II supernova, probably the most popular of the proposed sites, abundances of r-process elements may be altered by the intense neutrino flux. We point out that the effects would be especially pronounced for eight isotopes that can be efficiently synthesized by the neutrino reactions following r-process freeze-out. We show that the observed abundances of these isotopes are entirely consistent with neutrino-induced nucleosynthesis, strongly arguing for a supernova r-process site. The deduced neutrino fluences place stringent constraints on the freeze-out radius and dynamic time scale of the r process.
57 citations
TL;DR: In this paper, the authors use the shell model Monte Carlo method to calculate complete 0f1p-shell response functions for Gamow-Teller (GT) operators and obtain the corresponding strength distributions using a maximum entropy technique.
Abstract: We use the shell model Monte Carlo method to calculate complete 0f1p-shell response functions for Gamow-Teller (GT) operators and obtain the corresponding strength distributions using a maximum entropy technique. The approach is validated against direct diagonalization for 48Ti. Calculated GT strength distributions agree well with data from (n,p) and (p,n) reactions for nuclei with A=48–64. We also calculate the temperature evolution of the GT+ distributions for representative nuclei and find that the GT+ distributions broaden and the centroids shift to lower energies with increasing temperature.
40 citations
TL;DR: In this paper, the authors compare the results of the elementary particle model and the continuum random phase approximation (CRPA) and discuss whether experiments can decide which of them is correct, and show that the CRPA consistently reproduces inelastic electron scattering data at the excitation energies in 12 C probed by the LAMPF experiment.
21 citations
TL;DR: In this paper, the authors performed shell model Monte Carlo calculations of selected N = Z pf-shell nuclei with a schematic Hamiltonian containing isovector pairing and quadrupole-quadrupole interactions.
15 citations
TL;DR: In this article, the authors performed shell model Monte Carlo calculations of selected N=Z pf-shell nuclei with a schematic hamiltonian containing isovector pairing and quadrupole-quadrupole interactions.
Abstract: We perform Shell Model Monte Carlo calculations of selected N=Z pf-shell nuclei with a schematic hamiltonian containing isovector pairing and quadrupole-quadrupole interactions. Compared to realistic interactions, this hamiltonian does not give rise to the SMMC ``sign problem'', while at the same time resembles essential features of the realistic interactions. We study pairing correlations in the ground states of N=Z nuclei and investigate the thermal dependence of selected observables for the odd-odd nucleus Co54 and the even-even nuclei Zn60 and Ni60. Comparison of the present results to those with the realistic KB3 interaction indicates a transition with increasing temperature from a phase of isovector pairing dominance to one where isoscalar pairing correlations dominate. In addition, our results confirm the qualitative reliability of the procedure used to cure the sign problem in the SMMC calculations with realistic forces.
9 citations
01 Apr 1997
TL;DR: A new long baseline neutrino oscillation experiment is being built at the Palo Verde Nuclear Generating Station near Phoenix, Arizona as discussed by the authors, with a sensitivity of Δm 2 ~ 10−3 eV 2 and sin 2(2θ) ~ 0.1.
Abstract: A new long baseline neutrino oscillation experiment1 is being built at the Palo Verde Nuclear Generating Station near Phoenix, Arizona. Its sensitivity is Δm 2 ~ 10−3 eV 2 and sin 2(2θ) ~ 0.1. The lab construction has been finished, the detector installation is almost completed and we are about to take data soon.
6 citations